These studies represent a continuation of earlier work demonstrating that while frontal sensorimotor cortex is critical to the performance of an instrumental conditioned response, this response does not require the pyramidal tracts. A cortically influenced central feedback circuit was proposed for instrumental conditioning, involving neocortex, cerebellum and red nucleus. Recent studies generally support these postulations, and have added much detail to our understanding of central pathways in associative learning. Many questions remain, however, and the proposed studies are aimed at determining the extent to which conditioned limb responses are dependent upon a) corticorubral/corticopontine pathways; b) cerebellar cortex/deep cerebellar nuclei; c) rubrospinal tracts. Training procedures are similar to those described earlier, in which cats are conditioned (classical and instrumental) to flex the forelimb in response to a tone and/or light stimulus; the unconditioned stimulus is a shock to the same limb. Cerebellar cortical lesions are performed by subpial suction, using proven methods. Cerebellar nuclear lesions and rubrospinal tractotomy will be carried out stereotaxically, using kainic acid and radio frequency lesion techniques. A transbuccal approach will be used for cerebral peduncle transection. Studies of the sort described here will provide neurobiologists with information critical to the eventual understanding of normal and abnormal processes involved in learning and information storage, and should add another dimension to the rabbit NMR model by examining subcortical circuits using a cat limb flexion model. They will also begin to re-explore the role of the telencephalon in conditioned learning.